Detection of Abrin Holotoxin Using Novel Monoclonal Antibodies

Mass Spectrometric Detection and Differentiation of Enzymatically Active Abrin and Ricin Combined with a Novel Affinity Enrichment Technique

Abrin and ricin are toxic proteins produced by plants. Both proteins are composed of two subunits, an A-chain and a B-chain. The A-chain is responsible for the enzymatic activity, which causes toxicity. The B-chain binds to glycoproteins on the cell surface to direct the A-chain to its target. Both toxins depurinate 28S rRNA, making it impossible to differentiate these toxins based on only their enzymatic activity. We developed an analytical workflow for both ricin and abrin using a single method and sample. We have developed a novel affinity enrichment technique based on the ability of the B-chain to bind a glycoprotein, asialofetuin. After the toxin is extracted with asialofetuin-coated magnetic beads, an RNA substrate is added. Then, depurination is detected by a benchtop matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometer to determine the presence or absence of an active toxin. Next, the beads are subjected to tryptic digest. Toxin fingerprinting is done on a benchtop MALDI-TOF MS. We validated the assay through sensitivity and specificity studies and determined the limit of detection for each toxin as nanogram level for enzymatic activity and μg level for toxin fingerprinting. We examined potential cross-reactivity from proteins that are near neighbors of the toxins and examined potential false results in the presence of white powders.

Ultrafast protein digestion using an immobilized enzyme reactor following high-resolution mass spectrometry analysis for rapid identification of abrin toxin

Abrin toxin, highly dangerous with an estimated human lethal dose of 0.1-1 μg per kg body weight, has attracted much attention regarding criminal and terroristic misuse over the past decade. Therefore, developing a rapid detection method for abrin toxin is of great significance in the field of biosecurity. In this study, based on the specific dissociation method of an immobilized enzyme reactor, the trypsin immobilized reactor Fe3O4@CTS-GA-Try was prepared to replace free trypsin, and the immobilized enzyme digestion process was systematically investigated and optimized by using bovine serum albumin as the simulant of abrin. After 5 min one-step denaturation and reduction, a satisfactory peptide number and coverage were yielded with only 15 s assisted by an ultrasound probe to identify model proteins. Subsequently, abrin was rapidly digested using the established method, resulting in a stable and highly reproducible characteristic peptide number of 39, which can be analyzed by nanoelectrospray ionization coupled with high-resolution mass spectrometry. With the acquisition mode of full MS scan coupled with PRM, not only MS spectroscopy of total abrin peptides but also the corresponding MS/MS spectroscopy of specific abrin peptides can achieve the characteristic detection of abrin toxin and its different isoforms in less than 10 minutes, with high repeatability. This assay provides a universal platform and has great potential for the development of on-site detection and rapid mass spectrometric analysis techniques for macromolecular protein toxins and can further be applied to the integrated detection of chemical and biological agents.

Sensitive Detection and Differentiation of Biologically Active Ricin and Abrin in Complex Matrices via Specific Neutralizing Antibody-Based Cytotoxicity Assay

Ricin and abrin are highly potent plant-derived toxins, categorized as type II ribosome-inactivating proteins. High toxicity, accessibility, and the lack of effective countermeasures make them potential agents in bioterrorism and biowarfare, posing significant threats to public safety. Despite the existence of many effective analytical strategies for detecting these two lethal toxins, current methods are often hindered by limitations such as insufficient sensitivity, complex sample preparation, and most importantly, the inability to distinguish between biologically active and inactive toxin. In this study, a cytotoxicity assay was developed to detect active ricin and abrin based on their potent cell-killing capability. Among nine human cell lines derived from various organs, HeLa cells exhibited exceptional sensitivity, with limits of detection reaching 0.3 ng/mL and 0.03 ng/mL for ricin and abrin, respectively. Subsequently, toxin-specific neutralizing monoclonal antibodies MIL50 and 10D8 were used to facilitate the precise identification and differentiation of ricin and abrin. The method provides straightforward and sensitive detection in complex matrices including milk, plasma, coffee, orange juice, and tea via a simple serial-dilution procedure without any complex purification and enrichment steps. Furthermore, this assay was successfully applied in the unambiguous identification of active ricin and abrin in samples from OPCW biotoxin exercises.

Gaps in forensic toxicological analysis: The veiled abrin

Abrus precatorius is an herbaceous, flowering plant that is widely distributed in tropical and subtropical regions. Its toxic component, known as abrin, is classified as one of the potentially significant biological warfare agents and bioterrorism tools due to its high toxicity. Abrin poisoning can be utilized to cause accidents, suicides, and homicides, which necessitates attention from clinicians and forensic scientists. Although a few studies have recently identified the toxicological and pharmacological mechanisms of abrin, the exact mechanism remains unclear. Furthermore, the clinical symptoms and pathological changes induced by abrin poisoning have not been fully characterized, and there is a lack of standardized methods for identifying biological samples of the toxin. Therefore, there is an urgent need for further toxicopathologic studies and the development of detection methods for abrin in the field of forensic medicine. This review provides an overview of the clinical symptoms, pathological changes, metabolic changes, toxicologic mechanisms, and detection methods of abrin poisoning from the perspective of forensic toxicology. Additionally, the evidence on abrin in the field of forensic toxicology and forensic pathology is discussed. Overall, this review serves as a reference for understanding the toxicological mechanism of abrin, highlighting the clinical applications of the toxin, and aiding in the diagnosis and forensic identification of toxin poisoning.

Trends in the analysis of abrin poisoning for forensic purposes

Abrus precatorius is a poisonous plant known since ancient times. Accidental poisoning is more common due to the intake of plant seeds containing deadly abrin which is a highly toxic and a thermolabile plant toxalbumin. Abrin has also been reported to be a potential chemical agent that can be used as bioweapon in military or terrorism. Abrin is a ribosome inactivating protein that contains multiple isotoxic forms of protein subunits called chain A and B. The identification of this toxalbumin in the plant is important to determine cause of death in poisoning cases. Therefore, the present review focuses on the structure, mode of administration, tokicokinetics, extraction procedures and forensic analysis of abrin and other constituents. It is observed that most of the researchers have utilized immunological methods for the detection of plant components. This technique has proved to be more sensitive, reliable and accurate for the detection of extremely low concentrations of toxin.

A Self-Driven Microfluidic Chip for Ricin and Abrin Detection

Ricin and abrin are phytotoxins that can be easily used as biowarfare and bioterrorism agents. Therefore, developing a rapid detection method for both toxins is of great significance in the field of biosecurity. In this study, a novel nanoforest silicon microstructure was prepared by the micro-electro-mechanical systems (MEMS) technique; particularly, a novel microfluidic sensor chip with a capillary self-driven function and large surface area was designed. Through binding with the double antibodies sandwich immunoassay, the proposed sensor chip is confirmed to be a candidate for sensing the aforementioned toxins. Compared with conventional immunochromatographic test strips, the proposed sensor demonstrates significantly enhanced sensitivity (≤10 pg/mL for both toxins) and high specificity against the interference derived from juice or milk, while maintaining good linearity in the range of 10–6250 pg/mL. Owing to the silicon nanoforest microstructure and improved homogeneity of the color signal, short detection time (within 15 min) is evidenced for the sensor chip, which would be helpful for the rapid tracking of ricin and abrin for the field of biosecurity.

Neutralizing Monoclonal Antibody, mAb 10D8, Is an Effective Detoxicant against Abrin-a Both In Vitro and In Vivo

Abrin is a types II ribosome-inactivating protein (RIP) isolated from Abrus precatorious seeds, which comprises a catalytically active A chain and a lectin-like B chain linked by a disulfide bond. Four isotoxins of abrin have been reported with similar amino-acid composition but different cytotoxicity, of which abrin-a is the most potent toxin. High lethality and easy availability make abrin a potential bioterrorism agent. However, there are no antidotes available for managing abrin poisoning, and treatment is only symptomatic. Currently, neutralizing antibodies remain the most effective therapy against biotoxin poisoning. In this study, we prepared, identified, and acquired a high-affinity neutralizing monoclonal antibody (mAb) 10D8 with a potent pre- and post-exposure protective effect against cytotoxicity and animal toxicity induced by abrin-a or abrin crude extract. The mAb 10D8 could rescue the mouse injected intraperitoneally with a 25 × LD₅₀ dose of abrin-a from lethality and prevent tissue damages. Results indicated that 10D8 does not prevent the binding and internalization of abrin-a to cells but inhibits the enzymatic activity of abrin-a and reduces protein synthesis inhibition of cells. The high affinity, good specificity, and potent antitoxic efficiency of 10D8 make it a promising candidate for therapeutic antibodies against abrin.

[Highly toxic type Ⅱ ribosome-inactivating proteins ricin and abrin and their detection methods: a review]

Ⅱ型核糖体失活蛋白(RIPs)是一类重要的蛋白毒素,该类毒素大都具有一对二硫键连接的A-B链结构特征,B链具有半乳糖结合特性,能够与真核细胞膜表面受体特异性结合,将具有N-糖苷酶活性的A链导入细胞,与核糖体特定位点发生脱嘌呤作用使核糖体失活,最终通过抑制蛋白质合成而展现出细胞毒性。Ⅱ型RIPs毒素毒性极强,来源于植物的蓖麻毒素(ricin)和相思子毒素(abrin)的毒性分别是神经性毒剂维埃克斯(Vx)的385倍和2885倍。同时,该类毒素来源广泛、易于制备、稳定性好,成为一类潜在化生恐怖战剂,受到国内外广泛关注,其中蓖麻毒素作为唯一的蛋白毒素被收录于禁止化学武器公约禁控清单。近年来发生的多次蓖麻毒素邮件恐怖事件,进一步促进了有关Ⅱ型RIPs毒素的准确、灵敏、快速的检测鉴定技术的发展。剧毒性Ⅱ型RIPs毒素的检测鉴定方法主要涉及免疫分析法为代表的特异性识别和生物质谱分析为主的定性定量检测方法,以及基于脱嘌呤反应活性和细胞毒性的毒素活性检测方法。基于抗原-抗体作用的免疫检测法及基于寡核苷酸适配体的特异性识别检测法具有速度快、灵敏度高的优势,但对于复杂样品中高度同源蛋白的检测,易产生假阳性结果。随着生物质谱技术的快速发展,电喷雾离化(ESI)或基质辅助激光解吸离化(MALDI)等技术广泛应用于蛋白质的准确鉴定,不仅能够提供蛋白毒素的准确分子量和结构序列信息,而且能够实现准确定量。酶解质谱法是应用最为广泛的检测鉴定方法,通过酶解肽指纹谱分析,实现蛋白毒素的准确鉴定;对于复杂样品中蛋白毒素的分析,通过多种蛋白酶酶解策略获得丰富的特异性肽段标志物,然后进行肽段标志物的靶向质谱分析从而获得准确的定性及定量信息,方法有效提升了Ⅱ型RIPs毒素鉴定的准确度和灵敏度。免疫分析法和生物质谱法能够准确鉴定Ⅱ型RIPs毒素,但无法识别毒素是否还保持毒性。对于Ⅱ型RIPs毒素的活性分析,主要包括基于N-糖苷酶活性的脱嘌呤反应测定法和细胞毒性测定法,两种方法均可实现毒素毒性的简便、快速、灵敏的分析检测,是Ⅱ型RIPs毒素检测方法的有效补充。由于该类毒素的高度敏感性,国际禁止化学武器组织(OPCW)对相关样品中Ⅱ型RIPs毒素的分析提出了唯一性鉴定的技术要求。该文引用了Ⅱ型RIPs毒素及其检测方法相关的70篇文献,综述了以上Ⅱ型RIPs毒素的结构性质、中毒机理及典型剧毒性Ⅱ型RIPs毒素检测方法的研究进展,对不同检测方法的特点和应用潜力进行了总结,并结合OPCW对Ⅱ型RIPs毒素唯一性鉴定的技术需求,展望了未来Ⅱ型RIPs毒素检测技术研究的发展趋势。

Synthetic Biology-Empowered Hydrogels for Medical Diagnostics

Synthetic biology is strongly inspired by concepts of engineering science and aims at the design and generation of artificial biological systems in different fields of research such as diagnostics, analytics, biomedicine, or chemistry. To this aim, synthetic biology uses an engineering approach relying on a toolbox of molecular sensors and switches that endows cellular hosts with non-natural computing functions and circuits. Importantly, this concept is not only limited to cellular approaches. Synthetic biological building blocks have also conferred sensing and switching capability to otherwise inactive materials. This principle has attracted high interest for the development of biohybrid materials capable of sensing and responding to specific molecular stimuli, such as disease biomarkers, antibiotics, or heavy metals. Moreover, the interconnection of individual sense-and-respond materials to complex materials systems has enabled the processing of, for example, multiple inputs or the amplification of signals using feedback topologies. Such systems holding high potential for applications in the analytical and diagnostic sectors will be described in this chapter.

Rapid Differential Detection of Abrin Isoforms by an Acetonitrile- and Ultrasound-Assisted On-Bead Trypsin Digestion Coupled with LC-MS/MS Analysis

The high toxic abrin from the plant Abrus precatorius is a type II ribosome-inactivating protein toxin with a human lethal dose of 0.1-1.0 µg/kg body weight. Due to its high toxicity and the potential misuse as a biothreat agent, it is of great importance to developing fast and reliable methods for the identification and quantification of abrin in complex matrices. Here, we report rapid and efficient acetonitrile (ACN)- and ultrasound-assisted on-bead trypsin digestion method combined with HPLC-MS/MS for the quantification of abrin isoforms in complex matrices. Specific peptides of abrin isoforms were generated by direct ACN-assisted trypsin digestion and analyzed by HPLC-HRMS. Combined with in silico digestion and BLASTp database search, fifteen marker peptides were selected for differential detection of abrin isoforms. The abrin in milk and plasma was enriched by immunomagnetic beads prepared by biotinylated anti-abrin polyclonal antibodies conjugated to streptavidin magnetic beads. The ultrasound-assisted on-bead trypsin digestion method was carried out under the condition of 10% ACN as denaturant solvent, the entire digestion time was further shortened from 90 min to 30 min. The four peptides of T3A^a,b,c,d, T12A^a, T15A^b, and T9A^c,d were chosen as quantification for total abrin, abrin-a, abrin-b, and abrin-c/d, respectively. The absolute quantification of abrin and its isoforms was accomplished by isotope dilution with labeled AQUA peptides and analyzed by HPLC-MS/MS (MRM). The developed method was fully validated in milk and plasma matrices with quantification limits in the range of 1.0-9.4 ng/mL for the isoforms of abrin. Furthermore, the developed approach was applied for the characterization of abrin isoforms from various fractions from gel filtration separation of the seeds, and measurement of abrin in the samples of biotoxin exercises organized by the Organization for the Prohibition of Chemical Weapons (OPCW). This study provided a recommended method for the differential identification of abrin isoforms, which are easily applied in international laboratories to improve the capabilities for the analysis of biotoxin samples.

Differentiation, Quantification and Identification of Abrin and Abrus precatorius Agglutinin

Abrin, the toxic lectin from the rosary pea plant Abrus precatorius, has gained considerable interest in the recent past due to its potential malevolent use. However, reliable and easy-to-use assays for the detection and discrimination of abrin from related plant proteins such as Abrus precatorius agglutinin or the homologous toxin ricin from Ricinus communis are sparse. To address this gap, a panel of highly specific monoclonal antibodies was generated against abrin and the related Abrus precatorius agglutinin. These antibodies were used to establish two sandwich ELISAs to preferentially detect abrin or A. precatorius agglutinin (limit of detection 22 pg/mL for abrin; 35 pg/mL for A. precatorius agglutinin). Furthermore, an abrin-specific lateral flow assay was developed for rapid on-site detection (limit of detection ~1 ng/mL abrin). Assays were validated for complex food, environmental and clinical matrices illustrating broad applicability in different threat scenarios. Additionally, the antibodies turned out to be suitable for immuno-enrichment strategies in combination with mass spectrometry-based approaches for unambiguous identification. Finally, we were able to demonstrate for the first time how the developed assays can be applied to detect, identify and quantify abrin from a clinical sample derived from an attempted suicide case involving A. precatorius.

CCD Based Detector for Detection of Abrin Toxin Activity

Abrin is a highly potent and naturally occurring toxin produced in the seeds of Abrus precatorius (Rosary Pea) and is of concern as a potential bioterrorism weapon. There are many rapid and specific assay methods to detect this toxic plant protein, but few are based on detection of toxin activity, critical to discern biologically active toxin that disables ribosomes and thereby inhibits protein synthesis, producing cytotoxic effects in multiple organ systems, from degraded or inactivated toxin which is not a threat. A simple and low-cost CCD detector system was evaluated with colorimetric and fluorometric cell-based assays for abrin activity; in the first instance measuring the abrin suppression of mitochondrial dehydrogenase in Vero cells by the MTT-formazan method and in the second instance measuring the abrin suppression of green fluorescent protein (GFP) expression in transduced Vero and HeLa cells. The limit of detection using the colorimetric assay was 10 pg/mL which was comparable to the fluorometric assay using HeLa cells. However, with GFP transduced Vero cells a hundred-fold improvement in sensitivity was achieved. Results were comparable to those using a more expensive commercial plate reader. Thermal inactivation of abrin was studied in PBS and in milk using the GFP-Vero cell assay. Inactivation at 100 °C for 5 min in both media was complete only at the lowest concentration studied (0.1 ng/mL) while treatment at 63 °C for 30 min was effective in PBS but not milk.

Biological Toxins as the Potential Tools for Bioterrorism

Biological toxins are a heterogeneous group produced by living organisms. One dictionary defines them as "Chemicals produced by living organisms that have toxic properties for another organism". Toxins are very attractive to terrorists for use in acts of bioterrorism. The first reason is that many biological toxins can be obtained very easily. Simple bacterial culturing systems and extraction equipment dedicated to plant toxins are cheap and easily available, and can even be constructed at home. Many toxins affect the nervous systems of mammals by interfering with the transmission of nerve impulses, which gives them their high potential in bioterrorist attacks. Others are responsible for blockage of main cellular metabolism, causing cellular death. Moreover, most toxins act very quickly and are lethal in low doses (LD50 < 25 mg/kg), which are very often lower than chemical warfare agents. For these reasons we decided to prepare this review paper which main aim is to present the high potential of biological toxins as factors of bioterrorism describing the general characteristics, mechanisms of action and treatment of most potent biological toxins. In this paper we focused on six most danger toxins: botulinum toxin, staphylococcal enterotoxins, Clostridium perfringens toxins, ricin, abrin and T-2 toxin. We hope that this paper will help in understanding the problem of availability and potential of biological toxins.

Novel Phage Display-Derived Anti-Abrin Antibodies Confer Post-Exposure Protection against Abrin Intoxication

Abrin toxin is a type 2 ribosome inactivating glycoprotein isolated from the seeds of Abrus precatorius (jequirity pea). Owing to its high toxicity, relative ease of purification and accessibility, it is considered a biological threat agent. To date, there is no effective post-exposure treatment for abrin poisoning and passive immunization remains the most effective therapy. However, the effectiveness of anti-abrin monoclonal antibodies for post-exposure therapy following abrin intoxication has not been demonstrated. The aim of this study was to isolate high affinity anti-abrin antibodies that possess potent toxin-neutralization capabilities. An immune scFv phage-display library was constructed from an abrin-immunized rabbit and a panel of antibodies (six directed against the A subunit of abrin and four against the B subunit) was isolated and expressed as scFv-Fc antibodies. By pair-wise analysis, we found that these antibodies target five distinct epitopes on the surface of abrin and that antibodies against all these sites can bind the toxin simultaneously. Several of these antibodies (namely, RB9, RB10, RB28 and RB30) conferred high protection against pulmonary intoxication of mice, when administered six hours post exposure to a lethal dose of abrin. The data presented in this study demonstrate for the first time the efficacy of monoclonal antibodies in treatment of mice after pulmonary intoxication with abrin and promote the use of these antibodies, one or several, for post-exposure treatment of abrin intoxication.